TECHNICAL FIELD
This invention relates to inhalation devices for use with metered-dose aerosol canisters in inhalation therapy. In another aspect, this invention relates to inhalation devices that increase the fraction of drug that can be delivered in respirable form from an aerosol canister. In yet another aspect, this invention relates to inhalation devices that retain non-respirable particles. This invention further relates to methods of administering pharmaceutical formulations via inhalation therapy.